Historic Churches 2018

BCD SPECIAL REPORT ON HISTORIC CHURCHES 25 TH ANNUAL EDITION 25 installation of the fittings and all the associated electrical works can avoid or minimise interventions into historic fabric. The pre-planning phase of any lighting scheme should establish its feasibility and basic installation ground rules at the earliest opportunity. In a new-build environment, designers would develop full 3-D models of a space including details of all potential service ducts and cable routes. Refurbishment projects in more modern buildings are normally informed by comprehensive operation and maintenance manuals or O&Ms which include as-built drawings of the current or past installations. However, projects in historic buildings rarely have such a well-informed starting point. The available drawings might be hand-drawn or digitised from archive material, and few buildings over 100 years old were designed with service ducts compatible with modern requirements. As a result, when beginning work in a historic building it is often essential to commission a thorough, systematic investigation and on-site survey of the existing fixed wiring installation before the detailed design work starts. If as- built drawings exist they may be useful, provided they are checked for accuracy. This early enabling process will provide a clearer and more coordinated picture of what services and routes exist and where any new routes might be required. Only once the investigations have taken place can any invasive work be considered and this should only be done with the intention of minimising other disturbance to the historic fabric. Pre-existing accessible voids, slots, holes and service routes must, wherever possible, be reused to minimise additional permanent scarring to the building. If new openings are absolutely necessary, then everything must be done to ensure that as many services as possible share a common route through the building. This will minimise the loss of historic fabric and, along with designing-in spare capacity, will ensure that further loss of building fabric is contained, in the short term at least. Any and all such routes must be approved by the architect or surveyor before any works commence. HIDING NEW CABLING Where the building lends itself to offering suitable routes, a surface installation may sometimes be a viable solution, for example where mouldings, column capitals cornices or balustrades can disguise the presence of a carefully installed cable or conduit system. However, it is important to ensure that an installation of this type does not cover up, damage or otherwise interrupt the view of important building features and surfaces, nor should it create dirt traps or staining patterns from any resulting heat, moisture or air movement. Again, all such routes must be pre- approved by the architect or surveyor. Visible cabling, clips, junction boxes and any containment should be painted to match the surface finish as closely as possible. FIXINGS AND PATTRESSES The fixing and positioning of cable clips and brackets are also important. Positioning must respect the building’s requirements on spacing, rather than simply adhering to manufacturer’s guidelines or industry standards. Fixings should be made into material that is sacrificial rather than permanent, such as the mortar joints in stone or brickwork. Rather than fixing cable clips or conduit saddles at rigidly measured intervals, it may be necessary to have an irregular pattern that follows the spacing of the These lead cables, redundant since 1975, have been cut back at the edge of the rendered area. Fixings remain in the stonework where the cables have been removed but the rendered wall surface would have been very badly damaged had all of the cables been removed. Poor choice of cable route under an aisle ceiling: the junction box should have been fitted direct to the planking between the rafters with the cabling running along the top of the wall plate A mixture of twin and earth, fire resistant cabling and plastic trunking running around the west arch of a medieval tower An unfortunate route taken behind the hood mould of a window, damaging the stonework stone courses or other joints. The use of pin clips or any other fixings installed with hammers is to be avoided in most cases. With all installations, intervention should be kept to a minimum and strict observance to the principle of reversibility should be adhered to. Cables should be secured with screws fixed into timber or plastic plugs wherever possible. This principle applies equally to the fixing of any component within a building services system. For example, a light switch or a fire alarm break- glass unit may need the additional help of a pattress box, or other secondary support system, to enable the device to be fitted in the required location while allowing the mortar joints (or other preferred fixing locations) to be used. Timbers should not be drilled unless it is unavoidable, but at least such holes can be filled by wooden plugs or scarfing. The use of wood screws is far less damaging because their subsequent removal will leave less scarring and, if the screw did not remove any material in the first place, the timber will probably expand and refill the screw hole.